Microelectromechanical system (MEMS) devices often employ semiconductor fabrication techniques to create small mechanical structures on the surface of a substrate such as a wafer. In the production of MEMS gyroscopes and accelerometers, for example, such fabrication techniques are often used to create a number of moving structures that can be used to sense displacement and/or acceleration in response to movement of the device about an input or rate axis. In navigational and communications systems, for example, such moving structures can be used to measure and/or detect variations in linear and/or rotational motion of an object traveling through space. In other applications, such as automotive systems, for example, such moving structures can be used in vehicle dynamic control (VDC) systems and antilock braking system (ABS) to sense changes in vehicle and/or tire motion.
The packaging of such MEMS devices remains a significant hurdle in the overall fabrication process. In many cases, MEMS die include a MEMS side and a back side. The back side of the MEMS die is often bonded to the floor of a cavity in a MEMS package. Wire bond pads on the MEMS side of the MEMS die are typically wire bonded to bond pads in or along the MEMS package cavity. Finally, a package lid is typically secured to the top of the MEMS package to provide a hermitic seal for the MEMS package cavity. In some cases, the lid is secured in a vacuum or partial vacuum to provide a desired environment for the enclosed MEMS device. When a partial vacuum is used, and in some embodiments, an inert gas may be introduced when the lid is secured to the top of the MEMS package so that an inert gas is back filled into the enclosure housing the MEMS device, but this is not required.
Due to their size and composition, the mechanical structures of many MEMS devices are susceptible to damage in high-G applications, and from particles, moisture or other such contaminants that can become entrained within the MEMS package cavity. In addition, and in some cases, the difficulty in accurately regulating the pressure within the MEMS package cavity during the fabrication process can affect the performance characteristics of the MEMS device, often reducing its efficacy in detecting subtle changes in motion. As such, there is a need for robust packaging solutions for MEMS devices that offer superior vacuum performance and/or increased protection in some environments such as high-G environments, while also providing high volume throughput and low cost during the fabrication process.